Fluid pressure servomotor

ABSTRACT

A fluid pressure servo motor comprises a body having two operatively independent fluid chambers each chamber having therein a piston means movable in response to a fluid pressure differential so as to alter in use a two condition device from one to the other of said two conditions. The two piston means each have a lost motion means connection with the device to allow idle return of the pistons on cessation of the pressure differential. The two chambers and their respective pistons are co-axial and the pistons work in opposition to each other, one piston being fixed to a stirrup which bridges the other piston and acts in use against the two condition device, while allowing said other piston to move independently of the stirrup. Also disclosed is a vehicle door locking system incorporating servo motors as described.

This invention relates to fluid pressure servo motors that in use move atwo position device from one to the other of said two positions. Suchactuators are particularly useful for moving door lock mechanisms onmotor vehicles, from a locked condition to an unlocked condition or viceversa.

The use of vacuum operated servo motors for locking and unlocking ofmotor vehicle doors is well known. Examples of typical vacuum servomotors are illustrated in British Pat. Nos. 1,226,898 and 1,259,487. Theservo motors illustrated in these patents comprise two independentlyoperated fluid chambers separated by a single diaphragm which moves inresponse to a partial vacuum being created in one or other of the twochambers. The actuation rod which connects the diaphragm to the lockmechanism has to pass through an end wall of one of the fluid chambersand thus there is a problem with sealing the movable rod relative to thevacuum chamber wall.

The herein disclosed servo motor provides a construction in which theproblem of actuation rods moving relative to stationary seals has beeneliminated.

This invention also relates to multi-lock locking systems incorporatingsuch actuators.

According to this invention there is provided a fluid pressure servomotor having two operatively independent fluid chambers, each chamberhaving therein a piston means movable in response to a pressuredifferential so as to alter in use a two condition device from one tothe other of said two conditions and having a lost motion connectionwith said device to allow idle return of the piston means in the eventof cessation of the pressure differential wherein the two chambers andthe respective piston means therein are co-axial and move in oppositedirections in response to the pressure differential, and one pistonmeans is fixed to a stirrup which bridges the other piston means andacts in use against the two condition device, said other piston meansbeing able to move independently of the stirrup.

The term piston means also embraces other like means such as diaphragms.

Also according to this invention there is provided a multiple locklocking system with at least one servomotor as described above.

An embodiment of the invention will be described by way of example andwith reference to the accompanying drawings in which:

FIG. 1 shows above the centre line of a cross-section through aservomotor according to this invention and below the centre-line showsan elevation thereof; and

FIG. 2 is a schematic diagram of a locking system having servomotors asshown in FIG. 1.

With reference to FIG. 1 of the accompanying drawings a servo motor 11for moving a two condition device from one condition to the other, suchas a lock/unlock mechanism, comprises a stationary moulded plasticshousing 12 which has formed integrally therewith or attached thereto byany suitable means a bracket 13 for attaching said housing to a suitablesupport (not shown). The housing 12 has two co-axial independent fluidchambers 14 and 15 therein. The fluid chambers 14 and 15 areindependently connected by outlets 16 and 17, respectively, to a vacuumsource (not shown).

The first fluid chamber 14 houses a first piston 18, or like movablemember, which supports a rolling diaphragm 19. The diaphragm 19 seals atits outer periphery against the housing 12 and at its inner peripheryagainst the piston 18. The piston 18 is biased away from the wall 21 bya spring 20 acting therebetween. The movement of the piston 18 away fromthe wall 21 is limited by a ring 22 which also serves to crimp the outerperiphery of the diaphragm 19 against the housing 12.

The piston 18 also has a co-axial stem 23 projecting from the back facethereof (as shown). The stem 23 has an axially elongated slot 24therein; the slot 24 in use engaging loosely with a member 25 of a lockmechanism such that there is some axial play between the member 25 andthe ends of the slot 24. This loose play constitutes a lost motionconnection between the first piston 18 and the lock member 25.

The second fluid chamber 15 houses a second piston 26 also carrying adiaphragm 27 secured at its outer periphery to the housing 12 by acrimping ring 28 and sealing at its inner periphery against the piston26. A spring 29 biases the piston 26 away from the partition wall 21,such that the two pistons 18 and 26 are biased apart by the springs 20and 29, and when a vacuum or pressure reduction acts in one or other ofthe chambers 14 and 15 the respective piston is moved towards the wall21. Thus the two pistons can be said to be operating in opposition toone another.

The piston 26 is fixed to the inside of one leg of a stirrup 31 by asuitable clip 32 which bridges the housing 12 and first piston 18, sothat the other leg of the stirrup 31 provides a sliding support for thestem 23 thereof and its outside surface is an abutment surfaceengageable, in use, with the lock member 25.

The pressure servo motor shown in FIG. 1 is at the "rest" position. If apressure reduction, such as a vacuum, acts inside the first chamber 14,the first piston 18 is drawn in against the bias of the spring 20 thuspulling the lock member 25 towards the partition 21 counter to thedirection of arrow A until the member 25 abuts the outside of the secondleg of the stirrup 31. This is shown in dotted lines in FIG. 1. Assumingthis is the locking movement of member 25, when the vacuum is releasedthe piston 18 idly returns under the influence of the spring 20 andbecause of the lost motion connection between the slot 24 and the member25, this idle return can take place without disturbing the new lockedposition of the member 25. If the lock (not shown) to which the lockmember 25 is attached is now manually unlocked the member 25 can movealong the slot 24 without disturbing the servo motor.

To unlock the door a vacuum is created in chamber 15 and the piston 26moves towards the wall 21 against the spring 29. This moves the stirrup31 in the direction of arrow A so as to push the lock member 25 back upthe slot 24 and cause the locking mechanism to unlock. When the vacuumis released, piston 26 will idly return to its original position underthe influence of the spring 29. This creates a lost motion connectionbetween the member 25 and the stirrup 31 so that the lock (not shown)can now be manually locked without disturbing the servomotor.

With reference to FIG. 2, this shows a schematic diagram of a vehicledoor locking system utilizing the servo motors 11 as shown in FIG. 1. Avacuum reservoir 51 is connected via a one way valve 52 to the inletmanifold of an internal combustion petrol engine. The vacuum reservoir51 is connected by two separate conduits 53 and 54, via respectivesolenoid operated valves 55 and 56 to the locking and unlocking chambers14 and 15 respectively of a plurality of servomotors 11. In FIG. 2 onlytwo servomotors are shown but may be at least four servomotors, one perdoor lock on a four door car.

The power for the solenoids is provided by the battery 58 of the vehicleand the solenoid valves 55 and 56 are operated by central controlswitches, a first switch 59 accessible within the passenger compartmentof the vehicle and a second switch 62 associated with the driver's doorlock 61. There may also be another switch on the front passenger doorlock.

With the vehicle unlocked, as in FIG. 2, to lock the doors the solenoid56 only is energized to pull the associated valve away from thereservoir 51. This shuts off the air and connects the vacuum via theconduit 54 with first members 14 of the servomotors 11. The solenoid 56is actuated by either the spring loaded switch 59 within the car or bythe switch 61 associated with the driver's lock.

When a vacuum acts within the chambers 14 the associated lock members 25are moved counter to the direction of arrow A to lock all the respectivelocks. When the switch 59 or 61 is released the solenoid 56de-energizes, the associated valve moves to cut-off the vacuum andallows air to re-enter the conduits 54. The pistons 18 of the servomotorreturn to their original positions, as described previously, withoutdisturbing the locked state of the door.

To unlock the doors the solenoid 55 is energized, again through eitherof the spring loaded switches 59 or 61 which are moved to energize thesolenoid 55 without energizing the solenoid 56 at the same time. Thevalve associated with the solenoid 55 closes to shut off the air supplyand connect the vacuum reservoir with the chambers 15 of the servomotorsvia the conduit 53. This causes the pistons 26 to move the respectivestirrups 31 to return the lock members 25 in the direction of arrow Awithout disturbing the first pistons 18, since the lost motionconnection 24 accommodates such movement.

All doors have a normal manual operation, only the driver's door lock 62is shown with a manual over-ride 65 with the respective lock so that ifthe vacuum fails or the electrical supply to the solenoid fails thedriver's door can be locked or unlocked as is necessary.

I claim:
 1. A fluid pressure servo motor comprising:a stationary body;two co-axial fluid chambers defined within the body and which areseparated by a partition wall and are operatively independent; a pair ofco-axial piston means; each of said piston means being located in arespective one of said chambers and being movable towards the partitionwall in response to a pressure differential in the respective chamber,so as, in use, to effect alteration of a two condition device from oneto the other of said conditions and each piston means having a lostmotion means connection with said device to allow idle return of thepiston means in the event of cessation of the pressure differential; anda stirrup fixed to one of said two piston means and operatively bridgingthe other of said two piston means to act in use against said devicewhile allowing said other piston means to move axially independently ofthe stirrup.
 2. A servo motor as claimed in claim 1, wherein the stirrupslidably supports the piston means which it bridges.
 3. A servo motor asclaimed in claim 2, wherein the piston means bridged by the stirrup hasa stem with an axially elongated slot therein for engagement with saiddevice to move it into one condition when the bridged piston means isactuated, and the stirrup is engageable via an abutment surface thereonwith the device to return said device to its original condition onactuation of the piston means carrying the stirrup.
 4. A servo motor asclaimed in claim 1, wherein each piston means is spring loaded to returnto an "at rest" position when the pressure differential ceases.
 5. Adoor locking system for a motor vehicle including at least one servomotor as claimed in any proceeding claim.
 6. A door locking system asclaimed in claim 5, wherein the pressure differential across each pistonmeans is provided by a pressure reduction in the chamber relative to theatmosphere.
 7. A locking system as claimed in claim 6, wherein thelocking and unlocking operations of the servo motors are controlled by arespective solenoid-operated valve, for effecting the pressurereduction, and both solenoids are operated by a control switch whichengages only one solenoid, at any time, to cause the system to lock orunlock.
 8. A system as claimed in claim 7, wherein the servo motors areoperable from a first central switch accesible inside a vehicle to thedriver thereof and a second central switch is associated with the motorvehicle driver's door lock.